Our Hackers Group at CoderDojo Athenry made great progress last week on Project SABRE (Small Autonomous Battling Robotic Entities), in which two teams (Team DJARS and Team MEASAM) are building battlebots to compete with each other.

Here is a first test of the driving and steering of one of the bots, operated via a 2.4 GHz remote control with DSM2 protocol and an LemonRX receiver interfaced with an Arduino:

(The two teams worked together on the driving/steering code, which they will share.)

Team MEASAM’s bot has a flipper weapon, and they managed to get the actuator operating via the remote control last weekend also:

Meanwhile, Team DJARS have been working on their vertical spinner/grinder, which they are now controlling via a relay switch using the remote control also:

This project is proving to be a great and engaging learning experience!

25 March 2018 is the deadline if you would like to enter Coolest Projects, which will take place in Dublin on 26 May. You can find out information and register here: http://coolestprojects.org/

We have had lots of great participation from CoderDojo Athenry at Coolest Projects in the past few years, from our youngest members to our oldest, in all of our groups. People who enter find it a fun and rewarding day.

In the Hackers group this week, we took a large step forward in our Project SABRE (Small Autonomous Battling Robotic Entities), when we started working with remote controllers for our robots.

Components

From what the group has read, it looks like the most widely-used controllers are Spektrum-compatible DSMX or DSM2 ones. Therefore, we bought 3x Lemon RX DSMX/DSM2 receivers and one MLP4DSM Blade transmitter (as shown in the photo).

In recent weeks in the Hackers group, we have been refining our plans for Project SABRE (Small Autonomous Battling Robotic Entities).

Our mission for Project SABRE is to build “battlebots” that include some autonomous features. While there are many kits available for purchase, our two teams of hackers are designing and building their bots from scratch, identifying and sourcing all components ourselves, 3D printing bodies of their own designs, and programming everything themselves. Even the mentors are hands-off, helping mainly with project planning and purchasing, but not designing or making.

In the Hackers group, people worked on two different projects, making a Joule Thief and controlling motors.

Joule Thief

A Joule Thief is a small circuit that can boost the voltage from a small power source. Typically, it is used to power a 3-volt LED from a 1.5 volt battery. Because of how it works, it can continue to light the LED even when the battery would usually be considered to be “out of power”, when its voltage drops below 1v.

people in the group found various tutorials online, such as this one from Make Magazine: https://makezine.com/projects/joule-thief-battery-charger/

Motor Control with an Arduino

Continuing our work on Project SABRE, we were figuring out how to control motors.

A simple way to control the speed of a motor is to regulate its input voltage. In Arduino code, you set the output voltage of pins. However, you CANNOT just hook them up to the motor, as it will draw too much current and damage the Arduino.

The solution is to use a transistor: power from a 9V battery or the 5V USB power supply from an Arduino powers the motor with current flowing through the transistor, and we regulate the current flow by applying an appropriate voltage to the middle leg of the transistor.

Two more components are needed: a resistor for the middle leg of the transistor, and a diode to get rid of any voltage spikes that come from the motor acting as a generator if it us spun by hand, or when it is spinning down after current to it is cut.

This week in the Hackers group, rather than demonstrating how to use SketchUo, we showed some models that Kevin/Michael had built (see above), and the challenge was to recreate them. Some people got so far as to be able to print their models.

We also started some planning on an overall theme – more on that next time.

At this week’s session, Kevin introduced everybody to SketchUp, a free 3D modelling program. Models built with SketchUp can be exported to a format suitable for input into Repetier Host, to prepare them for 3D printing.

Incidentally, other options for 3D modelling include Blender (which some may have used previously for modelling) and TinkerCAD (which is web-based so does not require installation).

Here are some notes on getting started with SketchUp – they are taken from an NUI Galway summer camp I was involved in organising a couple of years ago: sketchupnotes

By the way, the picture above is a SketchUp model I built previously of a room.

Important: to export SketchUp models to Repetier, you first need to install the SketchUp STL Extension. Instructions:

n the SketchUp main menu, select Window – Extension Warehouse.

Search for SketchUp STL (see below), then go through the steps of downloading and installing.

Note that you may need to create a Trimble account (Trimble is the company that develops SketchUp).

You may see a warning that it is not marked as compatible with your version of SketchUp, but just press OK.

After installing the SketchUp STL extension, you will have a new menu item: File – Export STL.